1. Field of the Invention
The present invention relates to a hybrid power system with an external auxiliary motor, particularly to a hybrid power system having a small internal combustion engine and an external electric motor.
2. Description of Related Art
Conventionally, a vehicle is driven by an internal combustion engine. An internal combustion engine generates power that is transmitted to wheels to drive the vehicle. Since internal combustion engines operate by burning fuel, exhaust gas is produced, polluting air. For protecting the environment, electrically driven vehicles have been developed, having no internal combustion engines, but being driven by electric motors powered by batteries. In an electrically driven vehicle, electric energy stored in a battery is converted to mechanical energy by a motor. Mechanical power is by a gear transmitted to wheels. However, batteries have limited energy storage capabilities, so mileage of electrically driven vehicles is insufficient and generally do not meet motorists' demands. Electrically driven vehicles have therefore been sold only in small quantities and are not widely used. For this reason, vehicles driven by hybrid power systems have been developed, each having an engine and an electric motor. By suitable arranging of a transmission device, varying output of power is generated, with torque of the engine and the electric motor adapted appropriately to each other. Thus effective operation is achieved under various conditions, such as climbing, descending, braking and accelerating. An ideal combination of both motors results inefficient operation with high power output and low exhaust gas generation.
Due to a wide variety of transmission devices, hybrid power systems with varying components and varying effects exist. Currently, hybrid power systems are mostly used in four-wheel cars, with hundreds of systems having been developed and large competition between major car manufacturers.
However, small vehicles which are driven by small engines, like light motorcycles and minicars, have little space and need to be inexpensive. So it is difficult to install transmission devices for hybrid power systems of small vehicles. Consequently, very few hybrid power systems are used in small vehicles. Although some research is being done and several related inventions have been made, there is only a narrow range of applications of hybrid power systems of small vehicles.
A conventional hybrid power systems inmost cases has an electric motor directly connected with an output shaft of an engine, so that the electric motor and the engine drive a common axis, being placed next to the axis, consuming relatively large space. Furthermore, since the electric motor directly drives the axis, without any torque-enhancing gear, the electric motor is required to produce large torque and has consequently a large volume.
Besides, hybrid power systems have been designed which have driving systems between electric motors and engines. However, these driving systems are complicated or not effective.
In conventional art, several patents concerning hybrid power systems have been disclosed. Therein, an epicyclic train is taught, where a sun gear and planet gear is driven by an engine and an electric motor. Power output is at a ring gear. Since no torque converter is installed between the engine and the epicyclic train, any change of speed leads to jerks, with the engine and the electric motor not being adapted to each other. When the engine slows down, there is no way to interrupt power transmission. Thus this power transmission device is impractical.
Therefore, a hybrid power system for small vehicles is not only required to be accommodated in a small space, but also to allow for independent operation of the engine and the electric motor, as well as for smooth adaptation thereof to each other. Furthermore, it is desirable to regenerate electric energy by operating the engine and taking advantage of momentum of the moving vehicle. Then a comprehensive effect of the hybrid power system is achieved. At the same time, a direction of development of small power devices, as for motorcycles and minicars, is marked.